Changes in Ocean Circulation Could Lead To Rapid Regional Sea Level Change

Potsdam,
4 April 2005

One of the major consequences of future ocean circulation changes would be sea level change. This is shown in a new study by scientists from the Potsdam Institute for Climate Impact Research in Germany which was published in the recent issue of "Climate Dynamics". They investigated the scenario of a possible shutdown of the Atlantic overturning circulation and found this would cause up to one metre of sea level rise at coasts around the northern Atlantic, while sea level would drop in the South Atlantic. Compared to future sea level rise due to warming or ice melt, these changes could occur more rapidly, following the circulation changes almost without delay.

Sea level rise is widely discussed as a major consequence of future climate change. Global warming will lead to the melting of land ice, adding water to the global ocean. Furthermore, in a warming world sea water also warms and consequently expands. These two effects lead to a global sea level rise of some decimetres per century (the current rise as measured by satellites is 3 mm/yr) and pose a threat to many coastal areas. Now, researchers from the Potsdam Institute for Climate Impact Research (PIK) in Germany examined a different, possibly more rapid mechanism for changes in sea level (up to 25 mm/yr in some regions).

Due to the existence of ocean currents, the sea surface is not "flat" but has hills and valleys in balance with the Coriolis force associated with the currents. The sinking of deep water in the northern Atlantic, which is part of the Atlantic overturning circulation (or "conveyor belt") which keeps Europe warm, is associated with a particularly low sea level. Many scientists are concerned that this circulation could weaken or even cease altogether; the latter is widely considered a small, but non-negligible risk of global warming.

The new study shows that after a breakdown of this circulation, sea level in the northern Atlantic would rapidly increase by up to one metre, in addition to any global sea level rise caused by global warming. In the South Atlantic on the other hand, sea level would drop. Although these dynamic changes do not affect the global mean sea level, their regional effects on coastal areas of North America and Europe could be serious. This is a consequence of ocean circulation changes that has previously been largely overlooked, e.g., in the recent US Pentagon report discussing the implications of a similar scenario.

The Potsdam Institute for Climate Impact Research (PIK) was founded in 1992 and employs about 110 scientists. Its research on climate change, climate impacts and sustainable development is of international renown. PIK is a member of the Leibniz Association.